The invention relates to a sensor for the contactless scanning of labels, which are arranged at a mutual distance to each other, one after another, on a support material and are moved relative to the sensor, so that the labels are scanned successively by the sensor.
A sensor of this type is known from the DE 195 21 129 C1. This sensor is designed as capacitive sensor with two side-by-side arranged capacitor elements. The capacitor elements have respectively one air gap, in which the support material with the labels is guided. The distance between the capacitor elements is smaller than the dimensions for the labels in scanning direction. A time function element that generates a pulse sequence and a low pass filter are connected downstream after each capacitor element. The time function elements are activated with a time offset by way of an oscillator. The low-pass filter outputs are conducted to a differential amplifier. The edges of the labels can be detected with the signals that are present at the output of the differential amplifier.
However, these signals cannot provide information on whether the end or the beginning of a label was detected.
Furthermore, it is a disadvantage that the signals from the capacitive sensor are highly susceptible to interference caused by external influences such as moisture and temperature.
It is the object of the invention to design a sensor of the aforementioned type, in such a way that the labels on the support material can be detected as reliably as possible.
This object is solved with a sensor comprising a transmitter arranged at a distance to the labels for emitting transmission light beams which penetrate at least partially the labels and the support material, the sensor also comprising a receiving element, located opposite the transmitter and an evaluation unit for being coupled to at least the receiving element, wherein the receiving element comprises at least two receivers, arranged evenly spaced one after another in a movement direction of labels, such that a beam axis for the transmission light beams runs between the receivers, wherein when the transmission light beams fully strike a label or the support material, the transmission light beams run between the receivers and when a portion of the transmission light beams is deflected at an edge of a label, and is conducted inside of said label, said portion strikes one of the receivers and is evaluated in the evaluation unit for detecting the edges. Advantageous embodiments and useful modifications of the invention will become apparent from the disclosure herein.
In accordance with the invention, the sensor is designed as optoelectronic sensor. Its transmitter is arranged at a distance to the labels, onto which the transmission light beams, emitted by the transmitter, are directed. In accordance with a first alternative of the invention, the sensor operates with the transmitted-light method. For this, transmission light beams that penetrate the labels strike a receiving element, which is arranged on the side of the labels that is located opposite the transmitter.
The receiving element has two receivers, arranged one after another at a distance to each other in movement direction of the labels, so that the beam axis runs between the labels.
With this sensor, it is possible to securely detect transparent labels, which are affixed to a transparent support material or, to a limited degree, to a non-transparent support material.
If the transmission light beams strike a label or the support material between labels with their complete beam diameter, they penetrate this level surface and run between the receivers, without impinging on these.
This is preferably achieved in that the transmission light beams strike the labels or the support material at a right angle.
If the transmission light beams strike the edge of a label, then some of the transmission light beams are absorbed into the label as a result of diffraction or light refraction and progresses inside the label as a result of multiple reflections at the label surfaces.
In the process, a portion of the transmission light beams exits from the label and strikes one of the receivers. The receiving signal recorded in the receiver is used to detect the label edge in the evaluation unit.
The transmitted light is respectively guided to a specified receiver only, depending on whether the beginning or the end of a label is detected. Thus, by determining at which receiver the receiving signal is present, it is possible to determine whether the beginning or the end of a label was detected.
The use of an optical sensor is particularly advantageous since this sensor is insensitive against the effects of temperature and moisture.
The optical sensor has the additional advantage that the distance between transmitter and receiving element can be selected to be relatively large, which facilitates a handling of the sensor.
A second alternative of the invention provides that the transmitter and receiver are arranged on the same side of the support material with the labels. For this, the receivers are arranged in movement direction of the labels, on both sides of the transmitter. In this case, the light that is diffracted or refracted at the label edge is then introduced into the label. The respective receiver then detects the portion of the light that exits at the boundary layer of the label as a result of the multiple reflection.
One particularly advantageous embodiment of the invention provides for a third receiver, which is arranged in the beam axis for the transmission light beams, between the two first receivers. Non-transparent labels and support materials, such as paper, can be detected with this receiver.